Method and means for relating pressures in buffer and working spaces of a hot gas engine



Jan. 23, 1968 D. K. DORER 3,364,675

METHOD AND MEANS FOR RELATING PRESSURES IN BUFFER AND WORKING SPACES OF A HOT GAS ENGINE Filed Aug. 25, 1966 2 Sheets-Sheet 1 A T TOP/V5)" Jan. 23, 1968 D. K. DORER 3,364,675

METHOD AND MEANS FOR RELATING PRESSURES IN BUFFER AND WORKING SPACES OF A HOT GAS ENGINE Filed Aug. 25, 1966 2 Sheets-Sheet WORK/N6 6A5 E EUFFEA m PRESSURE I l l i r i t i I l I I? W a a I N. IN VEN'] OK. i flax 1e05 .flozez 5 4 j 3 x z B Y 8077044 DEAD Pan 2 PISTON FOS/T/O/V 0540 W CENTER CENTER United States Patent Ofiliee 3,354,675 Patented Jan. 23, 1968 3,364,675 METHGD AND lvIEANS FOR RELATING PRES- SURES 1N BUFFER AND WORKING SPACES F A HGT GAS ENGINE David K. Borer, Rochester, Mich, assignor to General Motors Sorporation, Detroit, Mich, a corporation of Delaware Filed Aug. 25, 1966, Ser. No. 575,102 13 Claims. (Cl. 6024) This invention relates to hot as apparatus such as a Stirling-cycle engine and more particularly to a method and means for relating pressures in chambers connecting with the power piston of such an engine.

A Stirling-cycle engine is a typical form of hot gas apparatus which is commonly provided with a cylinder having a power piston reciprocably mounted therein and connected through suitable mechanism to an output crankshaft. One end of the power piston is open to a working chamber filled with pressurized gas which is varied in pressure by cyclic heating and cooling so as to cause the power piston to reciprocate in the cylinder and deliver power to the output crankshaft.

In order to reduce the loads on the crank mechanism, it is known to provide a butter chamber open to the end of the piston opposite the working chamber and filled with gas pressurized to a desired level. The gas used is preferably of the same kind used as the working fluid.

Gas pressures in the working and buffer chambers vary in generally opposite cyclic fashion due to reciprocation of the power piston which alternately and oppositely expands and contracts the volumes of the two chambers. Pressures in the Working chamber are further aifected by the alternate heating and cooling of the gas previously mentioned.

Sealing means are provided to prevent excessive leakage of gas back and forth between the working and butter chambers during engine operation. It has been found, however, that properly controlled leakage between the chambers can be utilized to maintain butter pressures within a desired range with respect to the working pressures.

The present invention comprises a method for obtaining such control which permits the buffer pressure to be equalized with the working pressure at any desired point in the cycle, thus permitting maintenance of the bufier pressure range at any of a large number of possible levels with respect to the working pressure range. The invention further comprises means for carrying out this method which, when combined with a proper choice of chamber pressure levels, results in reduced pressure differentials across seal members and accordingly reduced friction losses and seal wear.

It is, therefore, an object of the present invention to provide a method of maintaining the buffer pressure substantially equal to the working gas pressure at one or more pro-selected points of the working cycle whereby a desired relationship between the butter and working gas pressures is maintained.

Another object of the invention is to provide a method for maintaining the average buffer pressure during the engine cycle at approximately the same level as the average working pressure during the same cycle.

A further object of the invention is to provide means associating the piston and cylinder of the engine to limit fluid flow between the working and buffer chambers during major portions of the engine cycle but to permit unidirectional flow between said chambers during at least one portion of said cycle.

Still another object of the invention is to provide means to limit fluid fiow between the working and buffer chambers of the engine during major portions of the engine cycle while permitting free flow in one direction between said chambers at a first pre-selected point of the engine cycle and permitting free flow in the opposite direction between said chambers at a second pre-selected point of the engine cycle.

Other objects and advantages of the invention may be clearly seen from the following description and drawings of a preferred embodiment selected for purposes of illustration and in which, referring to the drawings,

FIGURE 1 is a cross-sectional view of a Stirling-cycle engine embodying means according to the invention;

FIGURES 2 through 5 are enlarged cross-sectional views of the engine of FIGURE 1 showing the power piston at different positions of its stroke;

FIGURES 6 and 7 are further enlarged cross-sectional views of the engine of FIGURE 1 showing diagrammatically the operation of the one-way seals utilized on the power piston;

FIGURE 8 is a cross-sectional view taken in the plane generally indicated by the line 88 of FIGURE 2 and showing the cylinder bypass passage grooves;

FIGURE 9 is a pictorial view of a multi-piece oneway seal construction adapted for use in the engine and FIGURE 10 is a pressure volume diagram showing pressures in the working and butter chambers at all power piston positions of a complete engine cycle.

Referring more particularly to the drawings, FIGUR 1 illustrates a typical hot gas apparatus in the form of a Stirling-cycle engine generally indicated by numeral 29. The engine includes a cylinder 22 which may be formed in any suitable fashion and for illustrative purposes is shown to include a lower portion 24 and an upper portion 26 secured together by a threaded ring 28. A power piston 36 is reciprocably received in the lower portion 24 of the cylinder while a displacer piston 32 is reciprocably received in the upper portion 26.

A burner nozzle 34 extends into a pro-oxidation chamber 36 which is connected by means of swirl passages 38 to a combustion chamber 46. An air inlet 42 conveys air to the combustion chamber and an exhaust outlet 44 carries the air and products of combustion from the engine. Suitable heater tubes 46 in the combustion chamber 46 form a part of the working chamber 48 and communicate with the portion of the cylinder 22 above the displacer 32. A suitable regenerator 50 and cooler 52 are disposed adjacent the cylinder 22 and connect through heater tubes 46 the volumes within the cylinder above and below displaces piston 32. These volumes and components comprise the working chamber 48 and permit passage of the working fluid from one end of the upper portion 26 of the cylinder to the other in response to reciprocation of the displacer piston 32. An inlet passage 54 conveys coolant to an annular chamber 56 communicating with the cooler 52 and an outlet 58 conveys the coolant from the engine.

A buffer space 60 is provided in the lower portion 24 of the cylinder beneath the power piston 30 and in cornrnunication with an annular chamber 62 through suitable passages 64.

Pistons 3t) and 32 are connected for reciprocation in their respective portions of the cylinder 22 by a pair of crankshafts 56 rotatably connected by gears 68 and hav ing connecting rods 70 carried or crank throws 72 and pivotally attached to upper and lower yokes 74 and 76 respectively. Upper yoke 74 is secured to one end of connecting rod 78 which connects with the power piston 3% while lower yoke 76 is secured to connecting rod 89 which extends through connecting rod 78 and piston 30 and is secured to the displacer piston 32. Seals are provided at 82 to prevent leakage between the buffer space 69 and the crankcase 84 while other suitable seals (not shown) are located within piston 30 to prevent leakage between working chamber 48 and the crankcase 84. The above constnlction is all well known and represents a conventional manner of constructing a Stirling-cycle engine.

The diagram of FIGURE 10 is a typical plot of pressure in the working and buffer chambers versus power iston position under constant cycle operating conditions. However, to obtain such pressure relationships, it is, of course, necessary to provide sealing means between the power piston 30 and lower portion 24 of the cylinder to prevent excessive leakage of gas be ween the working and buffer chambers 48 and 6062 respectively. For this purpose, upper and lower seal rings 86 and 8'7 respectively are carried by the power piston and en age the inner surface or lower portion 24 of the cylinder. Also, longitudinally extending bypass grooves 88 are annularly spaced around the inner wall of lower portion 24 These bypass grooves combine with the seal rings 85 to control the relative pressures in the buffer and working chambers in a manner to be subsequently described.

FIGURE 9 shows a preferred construction of the seal rings 86, 87 for accomplishing the purposes of the present invention. Each ring comprises outer and inner ring 99 and 92 respectively. The outer ring has a stepped gap as at 94, while the inner ring has a straight gap as at 95 with a coil spring 98 hearing against the ends of the gap 9d to expand both inner and outer rings outwardly against the cylinder. Radial grooves 160 are formed along one face of the inner and outer rings.

As shown in FIGURE 2 the seal rings 86, 87 are installed in upper and lower grooves 102 and 104 respectively which are formed on the power piston and spaced apart a distance y. Upper ring 86 is located in upper groove 102 with its radial grooves 100 facing upwardly as shown in the figure while lower ring 87 is located in lower groove 104 with its radial grooves 100 facing downwardly. The two rings engage the surface of lower portion 24 of the cylinder thereby defining an intermediate space or volume 106 between them. The bypass grooves 88 are located in the cylinder such that in the bottom dead center position of the power piston, illustrated by FIG- URE 2, the grooves 88 are spaced at a distance x above the upper ring 86.

FIGURES 2 through illustrate the relation of the piston rings and bypass grooves at various positions of the power piston from top dead center (FIGURE 2) to bottom dead center (FIGURE 5). FIGURES 3 and 4 represent the piston positions at which the bypass grooves are aligned with the upper and lower seal rings respectively, the grooves being of sutficient length to permit free flow past the ring with which it is aligned. The power piston positions of FIGURES 25 are also indicated in FIG- URE so that the pressure relationships at these positions may be clearly understood.

OPERATION As the seal rings are installed in the piston grooves, their action under ordinary conditions, when both rings are in engagement with the cylinder wall, is to permit the free passage of gasoutwardly from intermediate space 106 to either the working space 48 or buffer space 60. Of course, such movement of gas occurs only if the pressure in either the working or buffer space is lower than that of the intermediate space.

The action of the rings is best shown by FIGURES 6 and 7 which represent lower ring 87 as installed in the engine. FIGURE 6 illustrates the condition when pressure in buffer space 60 is greater than that of intermediate space 106. Under this condition, the smooth upper face of ring 87 seats against the upper surface of groove 104 preventing free passage of gas from the buffer space 60 to intermediate space 106. When, however, pressure in intermediate space 106 exceeds that of buffer space 60, as illustrated in FIGURE 7, ring 87 is forced downwardly so that its lower surface, which contains radially extendmg grooves 100, seats against the lower surface of groove This provides a path for gas to pass through clearance spaces above and behind the ring and through radial groove I00 permitting free fluid flow sufficient to equalize pressures between spaces 106 and in a relatively short interval.

The action of the rings then when neither are being bypassed by grooves 88, as is the situation in FIGURES 2 and 5, is such that free flow is prevented in either direction between working space 48 and buffer space at since the rings adjacent these chambers will seek to prevent the escape of fluids therefrom. This action is, of course, subject to limited leakage which occurs due to the imperfect sealing capabilities of the rings.

When the piston moves to the position of FIGURE upper ring 86 is bypassed by grooves 88, permitting fr flow of fiuid between working chamber 48 and intermediate space 106. If at this point, therefore, pressure in the working space exceeds that of buffer space 60, flow will continue from intermediate space 106 past lower ring 87 into the buffer space so as to increase pressure in the buffer space in the direction of equalization with that of working space 48. If, however, pressure in the buffer space at position 3 is greater than that in the working space, no fiow will occur since lower seal 8% prevents substantial outflow of gas from buffer space 50.

In like manner, when the piston is in the position of FIGURE 4, flow is permitted from buffer space 60 to working space 48 if the buffer space pressure is higher, the result being a movement toward equalization of the two pressures. However, if the working space pressure is higher at this position, no flow will occur between the spaces.

Referring now particularly to FIGURE 10, a desired relationship of the working gas pressures and the buffer pressures is disclosed. Note that, due to heating and cooling of the working gas, the working pressure forms a closed curve on the pressure-volume diagram while the buffer pressure follows substantially a single line of adiabatic expansion and contraction. The relationship of these pressures is controlled by the above-described arrangement in the following manner.

When the piston is at bottom dead center (FIGURE 2), the working gas pressure is at the point indicated A While the buffer pressure is at its highest value.

Movement of the power piston upwardly a distance equal to dimension x raises the working pressure to point B and aligns the top ring 86 with bypass grooves 88 (FIGURE 3). However, since the buffer pressure is higher than the working pressure at this point, no flow occurs between these spaces.

Further upward movement of the power piston a distance equal to dimension y raises the working pressure to point C and aligns the lower ring 87 with bypass grooves 88 (FIGURE 4). At this point, the working and buffer pressures should be equal; however, if the buffer pressure is higher than the working pressure at this point, flow is permitted from buffer space 60 to working space 48 to equalize the pressures in these spaces. Of course, if the buffer pressure is lower than the working pressure, no flow occurs.

Movement of the piston to the top dead center position raises working gas pressure to point D and lowers the buffer pressure to its lowest point (FIGURE 5). No flow occurs at this condition due to the sealing action of the rings.

As the power piston moves downwardly, working pressure is reduced to point E while the lower ring is again aligned with the bypass grooves (FIGURE 4). No fiow occurs here since the working gas pressure is higher than the buffer pressure at this point.

Further downward movement of the power piston reduces working gas pressure to point F where the upper ring is aligned with grooves 88 (FIGURE 3). At this point, working and buffer gas pressure should again be I 5 equal; however, if the bufier pressure is lower than the working gas pressure, flow between the chambers is permitted in the direction of equalizing the pressures. If the buffer pressure is higher at this point, of course, no flow is permitted. As the power piston again moves downwardly, the working gas pressure returns to position A (FIGURE 2) and no flow is permitted between chambers due to the sealing action of the rings.

As a result of the above-described action, the working gas and buffer pressures are permitted to follow their own independent cycles during the major portion of movement of the power piston. However, the buffer pressure is related to the working gas pressure at points C and F where it is desired that these pressures be equal. At point C excessive bufiFer pressures are reduced to obtain equalization with the working pressure while at point F deficient buffer pressures are increased to obtain equalization pressure with the working pressure.

It should be apparent that by proper selection of the dimensions x and y, which determine the relative positions of the power piston at which the upper and lower rings are aligned with bypass grooves 88, the butter pressure may be made to operate in any desired range of the working gas pressure as long as it is equal to the working gas pressure during at least one point of the working cycle.

It should also be apparent that suitable control under certain conditions may be obtainable by cooperative action of the bypass grooves 88 with only one of the two sealing rings. This would be the case wherever the relative pressure values of the working and buffer pressures are such that residual leakage of the rings in their sealing positions tends to move the buffer pressure in a direction opposite to the direction of equalization flow permitted by the cooperation of the single ring with the bypass grooves.

With the disclosed ring arrangement, it has been found desirable to maintain the average butler pressure in a range approximately equal to the average working gas pressure. This tends to equlize the maximum positive and negative difierential pressures between the working and buffer chambers. Since the intermediate space tends to follow generally the lower of the two pressures, this results in substantially equal maximum differential pressures across the upper and lower seals, reducing the maximum diflerential pressures reached. The result is to reduce and equalize the wear on the two seals and to reduce the friction loss caused by the seals, rubbing against the cylinder wall.

While the foregoing description is of a preferred embodiment of the invention, numerous changes may be made by those skilled in the art within the spirit and scope of the invention which is intended to be limited only by the language of the following claims.

I claim:

1. For use with a hot gas engine having working and buffer chambers filled with compressible fluid and connected by a cylinder, and a piston reciprocably disposed in said cylinder between said chambers,

a method for maintaining the buffer pressure approximately equal to the working pressure at a predetermined point of the working cycle characterized by the steps of (a) sealing the piston for unidirectional fluid flow between one end and the center, subject to limited leakage,

b) sealing the piston for opposite unidirectional flow between the other end and the center, subject to limit-ed leakage, thereby defining an intermediate space associated with the piston and having free flow in one of two bidirectional'modes namely into and out of said space and subject to limited leakage in the other of said modes, and

(c) opening said intermediate space to one of said ends at least once each cycle and at a predetermined point therein, permitting flow in one direction between said chambers for a time sufficient to effect a substantial pressure change in the direction of equalization of pressures.

2. A method as defined in claim 1 wherein the step of opening said intermediate space to one of said ends is arranged to occur at a point of the working cycle such that the average buffer pressure over the cycle is maintained approximately equal to the average working pressure over the same cycle.

3. A method as defined in claim 1 and characterized by additional step of (d) opening said intermediate space to the other of said ends at least once each cycle and at a predetermined point therein distinct from said first predetermined point, permitting flow in the other direction between said chambers for a time sufiicient to efiect a substantial pressure change in the direction of equalization of pressures.

4. A method as defined in claim 3 wherein the predetermined points of the working cycle at which occur the steps of opening said intermediate space to one and then the other of said ends are selected to lie along a single line of adiabatic expansion and contraction of the buffer chamber volume over its cycle.

5. A method as defined in claim 4 wherein said predetermined points are selected such that the average bufier pressure over the cycle is maintained approximately equal to the average working pressure over the same cycle.

6. A method for relating pressures in the working chamber and buffer chamber of an external combustion hot gas engine having a cylinder member connecting said chambers and a piston member reciprocable in said cylinder memher, said method comprising the steps of (a) preventing free flow of fluid between said chambers during the major portion of the stroke of said piston while (b) permitting relatively free unidirectional fluid fiow between said chambers at a first predetermined position of said piston stroke.

7. A method for relating pressures in the working chamber and buffer chamber of a hot gas engine having a cylinder member connecting said chambers and a piston member reciprocable in said cylinder member, said method comprising the steps of (a) preventing free flow of fluid between said chambers during the major portion of the stroke of said piston while (b) permitting relatively free unidirectional fluid flow between said chambers at a first predetermined position of said piston stroke and (c) permitting relatively free unidirectional fluid flow between said chambers at a second predetermined position of said piston stroke distinct from said first position, free how at said second position being opposite in direction to free fiow at said first position.

8. The method of claim 7 wherein the predetermined positions of the piston stroke at which relatively free unidirectional fiuid fiow is permitted between said chambers are selected to equalize the working and butter pressures at points lying along a single line of adiabatic expansion and contraction of the butter chamber volume over its cycle.

9. The method of claim 8 wherein said predetermined positions are selected such that the average buffer pressure over the cycle is maintained approximately equal to the average working pressure over the same cycle.

10. In a hot gas engine having a working chamber and a butter chamber connected by a cylinder member and a piston member reciprocable in said cylinder member, means cooperating with said piston and cylinder members to normally resist fiuid flow between said chambers but to permit free unidirectional fluid flow between said chamers in at least one position of said piston member, said means comprising seal means in one of said piston and cylinder members and engaging the other and bypass means in said other member and arranged to cooperate with said seal means at said one piston position to permit fluid flow from one of said chambers to the other.

11. The combination of claim 10 wherein said seal means comprise a pair of longitudinally spaced one-way seal rings carried between said piston and cylinder members by one of said members and engaging the surface of the other, said seal rings defining an intermediate volume therebetween and being arranged to normally resist free fluid flow in one of two bidirectional modes, namely to said intermediate volume from said chambers and from said intermediate volume to said chambers, and to permit free fluid flow in the other of said modes and said bypass means comprise at least one longitudinally extending groove in said other member and positioned to bypass one of said rings at a predetermined position of piston movement to permit free bidirectional fiuid flow between said intermediate volume and one of said chambers.

12. The combination of claim 11 wherein said seal rings are carried by said piston and arranged to normally resist 8 free fluid flow from said chambers into said intermediate volume and to permit free fluid flow from said intermediate volume to said chambers.

13. The combination of claim 12 wherein said rings are spaced apart a predetermined distance less than the stroke of said piston and said groove is positioned to bypass the other of said rings at a second predetermined position of piston movement distinct from said first predetermined position to permit free bidirectional fiow of fluid between the other of said chambers and said intermediate volume.

References Cited UNITED STATES PATENTS 854,082 5/1907 Hooper et al. 123-74 1,229,217 6/1917 Brougham 12374 3,077,732 2/1963 Reinhart et a1. 60-24 3,319,416 5/1967 Renshaw 6024 FOREIGN PATENTS 372,966 4/1923 Germany.

WENDELL E. BURNS, Primary Examiner. 

10. IN A HOT GAS ENGINE HAVING A WORKING CHAMBER AND A BUFFER CHAMBER CONNECTED BY A CYLINDER MEMBER AND A PISTON MEMBER RECIPROCABLE IN SAID CYLINDER MEMBER, MEANS COOPERATING WITH SAID PORTON AND CYLINDER MEMBERS TO NORMALLY RESIST FLUID FLOW BETWEEN SAID CHAMBERS BUT TO PERMIT FREE UNIDIRECTIONAL FLUID BETWEEN SAID CHAMBERS IN AT LEAST ONE POSITION OF SAID PISTON MEMBER, SAID MEANS COMPRISING SEAL MEANS IN ONE OF SAID PISTON AND CYLINDER MEMBERS AND ENGAGING THE OTHER AND BYPASS MEANS IN SAID OTHER MEMBER AND ARRANGED TO COOPERATED WITH SAID SEAL MEANS AT SAID ONE PISTON PO- 